Aerospace structures adhesives mechanisms

In this brief review, we have attempted to demonstrate the importance of chemistry to the developments of new (or new forms of) adhesive materials. Much success has been achieved in the syntheses of polymers for aerospace adhesives and sealants. New or modified structural adhesives have been developed with improved mechanical properties and durability. However, there is still room for innovation for developing new adhesive materials for use under severe environments. 

Civil Electronics, automobile, aircraft, mechanical engineering, aerospace, medical, fuel cell, environmental science Wire insulation, tape, chip carrier, switches, liquid crystal display panels, foam insulation, baffles, bushings, seal rings, abrasive cutting wheels, composite structures, adhesives, gas separation membrane, high-temperature adhesive for semiconductor industries, pacemakers, eye lens implants, fuel cell membrane... 

Appiications aerospace, composites, electronics (mostly films and coatings), foam composites, hollow fiber membranes, electronics, fibers, mechanical parts (bearings, piston rings, valve seats, washers), microprocessor chip carriers, non-lubricated applications, nuclear power plants, photosensitive materials for positive imaging, photovoltaic film, solar cells, space shuttle, structural adhesives, ultrafiltration membranes ... 

Abstract. This chapter is concerned with an in-depth examination of the adherend surface pretreatments used prior to structural adhesive bonding. It encompasses the various substrates encountered, particularly but not exclusively, in the aerospace industry. It compares and contrasts mechanical, chemical and electrochemical methods used for substrates comprising aluminium alloys, titanium, stainless steel, thermoplastic and thermoset fibre reinforced composites and non-metallic honeycomb. Scanning and transmission electron microscope techniques are used to analyse and characterise many of the pretreated surfaces so produced. 

Pis are finding increased use in aerospace and automotive applications as structural adhesives due to their excellent mechanical property retention at elevated temperatures. Another major area of PI usage is the electrics/electronics industry. They are used as thermal and electrical insulators due to their excellent hard radiation resistance and good insulation... 

Adhesives and sealers can be an important part of a total corrosion protection system. Structural bonding procedures and adhesives for aluminum, polymer composites, and titanium are well established in the aerospace industry. Structural bonding of steel is gaining increasing prominence in the appliance and automotive industries. The durability of adhesive bonds has been discussed by a number of authors (see, e.g., 85). The effects of aggressive environments on adhesive bonds are of particular concern. Minford ( ) has presented a comparative evaluation of aluminum joints in salt water exposure Smith ( ) has discussed steel-epoxy bond endurance under hydrothermal stress Drain et al. (8 ) and Dodiuk et al. (8 ) have presented results on the effects of water on performance of various adhesive/substrate combinations. In this volume, the durability of adhesive bonds in the presence of water and in corrosive environments is discussed by Matienzo et al., Gosselin, and Holubka et al. The effects of aggressive environments on adhesively bonded steel structures have a number of features in common with their effects on coated steel, but the mechanical requirements placed on adhesive bonds add an additional level of complication. 

Mechanical attachment of components, devices, and other parts of an electronic assembly is the prime function of adhesives. Although adhesives are expected to bond a wide variety of materials for electronic applications, they do not need to be structural. They should, however, meet minimum tensile and shear strengths in order to withstand mechanical shock, thermal shock, thermal cycling, and vibration as specified for the intended application. For consumer and commercial products, these stresses may be minimal. For high reliability aerospace and medical systems, more severe tests as defined in MIL-STD-883 and other documents must be used. 

An adhesively bonded joint is typically more structurally efficient than a mechanically fastened joint. Fasteners introduce discrete, or at least concentrated, points at which load is transferred from one component to another. Therefore the peak stress at each fastener is much higher than overall joint stress and the joint must be suitably designed to withstand these peak stresses. Compounding this is the fact that aerospace components are typically quite thin with proportionately low fastener bearing strength. The most efficient way to mechanically fasten thin members is with numerous small fasteners which add weight and cost. 

Since the first symposium on Recent Advances in Adhesion, held September, 1971 in Washington, D.C., this Division of the American Chemical Society has continuously sponsored several symposia on adhesion and adhesives. The chemists have gradually realized the importance of adhesion in various fields of science and technology. During these years, the science of adhesion has steadily grown along with progress in surface science and fracture mechanics. Moreover, new adhesives have been invented and applied in actual structures, for example, structural and aerospace adhesives. 

Bonded joints are extensively employed in the construction of composite structures in aerospace applications, maritime structures, lifting equipment, wind mills as well as automotive industries [3, 4, 5], Unlike the bolt hole in mechanical fastening that causes a stress concentration in the composite joint plates, adhesively bonded joints minimize the potential for stress concentration within the joint. Besides, applications where lower structural weight, improved damage tolerance design philosophy are required, adhesively bonded joints provides a potential solution. Bonded joints are an efficent fastening solution also for hybrid structures, i.e., structures where composite parts are connected to metal parts. 

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